package com.pavlinic.mylisp;


public class SymbolExpression implements Expression {

  private final String value;

  public SymbolExpression(String value) {
    this.value = value;
  }

  @Override
  public String toString() {
    return value.toString();
  }

  public Expression evaluate(EvaluationContext context) {
    final Expression boundValue = context.getBinding(value);
    if (boundValue == null && !context.hasBinding(value)) {
    	throw new NoSuchBindingException(value);
    }
	return boundValue;
  }

  public String getValue() {
    return value;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((value == null) ? 0 : value.hashCode());
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    SymbolExpression other = (SymbolExpression) obj;
    if (value == null) {
      if (other.value != null)
        return false;
    } else if (!value.equals(other.value))
      return false;
    return true;
  }
  
}
